Production of strip material from powder



Oct. 13, 1964 B. CLARK PRODUCTION OF STRIP MATERIAL FROM POWDER 3 Sheets-Sheet 1 Filed NOV. 8, 1961 Oct. 13, 1964 KB. CLARK 3,1

PRODUCTION OF STRIP MATERIAL FROM POWDER Filed Nov. 8. 1961 5 Sheets-Sheet 2 JF p p-z,

Oct. 13, 1964 K. B. CLARK 3,152,892

PRODUCTION OF STRIP MATERIAL FROM POWDER Filed Nov. 8, 1961 5' Sheets-Sheet s United States Patent sasassz PRODUTJTIQN 0F TRiP MATERHAL FRQM PGWDER Kenneth B. Clark, Spragueville, 12.1., assignor to Texas Instruments Incorporated, Dailas, Tex., a corporation of Delaware Filed Nov. 8, 1961, Ser. No. 151,42t) 6 Claims. (Cl. 75-214) This invention relates to the production of strip material from powder, and with regard to certain more specific features, to the production of metallic strip material by solid-phase bonding of metal powder.

Among the several objects of the invention may be noted continuous-type production of strip material from powder in both clad and unclad forms in greater thicknesses of powder than heretofore obtainable; the production of metallic strip material in which the bonded powder is more densely compacted and flexible; and the production of metallic strip material Without edge-cracking and which has closer longitudinal and transverse tolerances than heretofore obtainable. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, ingredients and combinations of ingredients, and proportions thereof, steps and sequence of steps, features of construction, composition and manipulation, and arrangements of parts which will be exemplified in the constructions, products and methods hereinafter described, and the scope of which will be indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

FIG. 1 is a diagrammatic side elevation illustrating one form of the invention;

FIG. 2 is an enlarged detail section of certain roll gripping parts of FIG. 1;

FIG. 3 is a further enlarged section taken on line 33 of FIG. 2, showing certain roll contours;

FIG. 4 is an enlarged cross section taken on line 4-4 of FIGS. 1 and 2, showing one form of product made according to the invention;

FIG. 5 is a view similar to FIG. 4, showing a second form of product;

FIG. 6 is a view similar to FIG. 1, showing another form of the invention; and

FIG. 7 is an enlarged cross section taken on line 77 of FIG. 6, showing a third form of product.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Hereinafter the term powder means a finely divided material which, if a metal, may be sintered. The term metal includes alloys thereof. The term strip means any flexible sheet of appropriate width, thickness and length for bending at compression rolls and adapted to be coiled.

It is known to form strip by compression of finely divided (powdered) particles. Sometimes compression takes place against a backing strip, whether or not such a strip is retained in the final product. Heretofore the backing strip has entered the nip space between compression rolls along a trajectory extending substantially perpendicularly to a line between the roll centers, with the consequent disadvantage that powder was excessively pushed away from the rolls and only a limited thickness of compressed powder could be obtained. Edge-cracking due to transverse flow from straight rolls also presented a problem. Attempts to increase thickness and minimize edge-cracking were concerned primarily with changes in 3,152,892 Patented Get. 13, 1964 roll diameters, roll finishes and speeds, types and fineness of particle employed, and the like. Such variations produce relatively small improvements.

According to the present invention, a backing strip is substantially nonperpendicularly introduced to the roll nip space, so that it wraps partially around one roll and powder is fed between that roll and such strip in the wrapping range. This wrap-around feature decreases the amount of powder pushed aside by the roll, so that more powder is retained for compression against the baclcing strip. The rolls are arranged with male and female interlocking flange and groove portions for the stripand powder to provide substantially uniform compacted powder density transversely of the strip which advantageously contributes to preventing edge-cracking. The groove confines the backing strip and powder in the wrapping range and at the nip space so that transverse flow of strip and powder material is prevented, as well as the former undesirable edge-cracking. Means is also provided for effectively releasing the compressed backing and powder materials from the containing roll groove. After compression, the material is sintered, with or without the backing strip, to produce hacked or unbacked strip material, as desired. The invention has particular advantages in the manufacture of metal strip made from metal powder and metal strip, or from metal powder only.

Referring now more particularly to FIGS. 14 of the drawings, there is shown at numeral 1 a metal baclc ing strip extending from a coil 3 and over a guide roll 5. At 7 is shown diagrammatically an adjustable friction brake operative upon the strip, from which it passes to a guide roll 9. The strip l is resistance heated in approach to the guide roll 9 by means of current fed to it from an electrical circuit 11. The circuit is connected through a sliding contact 13 and a suitable contact means with the guide roll 9, as indicated at 15. At numerals 17 and 3.9 are shown compression rolls set to provide a nip region at 21 therebetween. The strip 1 is fed from the guide roll 9 to this nip region, then passes from the nipregion 21 over a suitable guide member 23 to a wind-up coil 25, the latter being suitable for placement in a furnace for subsequent sintering.

Referring now more particularly to FIGS. 2 and 3, it will be seen that the compression rolls 17 and 19 have interlocking forms at the nip space 21. Thus roll 19 contains a groove 27 having parallel fiat side walls 29, terminated by inwardly converging wall portions 31 which meet at very small fillets with a fiat cross-sectional bottom surface 33. Surface 33 is part of the cylindrical circumferential periphery of the bottom of groove 27 in roll 1a.

The mating roll 17 is provided with a flange 35 also having parallel flat side walls 37 closely fitting the parallel side Walls 29 of the groove 27. The rim of the flange 35 terminates in a transverse flat surface 39 which defines a cylindrical periphery for flange 35, the innermost extent of which lies tangentially at the transition between the walls 29 and 31. Thus the effective nip space between the rolls 17 and 1 is of quadrilateral cross section determined by the parallel lines 33, 39 and lines 31, as shown in FIG. 3. Surfaces 33 and 39 need not always be such as to roll out transverse parallel flat surfaces and may in some cases assume other shapes to roll out concave or convex surfaces. The purpose of this arrangement is to contain the backing strip 1 with compressed powder ll-C thereon, obtained from a supply of loose powder 41L. The loose powder ll-L is received in the groove 27 and under strip 1 from a main hopper 43 to which is attached a vibrator 45. An auxiliary hopper 47 supplies powder to the main hopper 43, so as to maintain a constant level in the latter. At numeral 49 is shown a stripping finger extending into the groove 2'7 of the roll 19 for releasing and guiding greases material therefrom. Numerals Sl designate felt lubricant pads for lubricating the top of the flange 35 and the groove 27.

By proper location of the guide roll 9, the backing strip 1 is led nonperpendicularly into the nip space 21 at an angle A, measured with respect to the center line C-L between roll centers. This angle A is substantially less than a right angle and sufiicient that a wraparound efiect is obtained over a considerable angular range with respect to the roll 19 of the material entering the nip space 21. As will be seen from FIG. 2, the outlet 53 of the hopper 43 is arranged to feed between the roll 19 and the entering strip, so as to feed loose powder into the wrap-around range. A preferable angle at A is on the order of 82 or substantially less. An angle of 80 is shown. In general, the smaller the angle A, the greater the thickness of powder that may be trapped for compression. Lar er angles A, viz smaller deviations from 90, will result in smaller increases in powder thicknesses, such, however, being sometimes desirable. An appropriate included angle of convergence between the surfaces 31 is, for example, 14, as shown at D in FIG. 3. The rolls 17 and 19 form a part of a suitable powerdriven adjustable rolling mill, the details of which are not shown because known to those skilled in the rolling art. Thus the rolls have the usual means for accomplishing adjustments of speeds, distances between centers, et cetera.

Operation O1 the form shown in FIGS. 1-4 is as follows:

Assume a strip 1 composed, for example, of a silverclad nickel base. The strip 1 in its coil form 3 is presumed to have had gross contaminants removed therefrom. Power drive of the rolls 17 and 19 draws the strip 1 from coil 3 and roll 5 through the brake 7 and over guide roll 9. The brake 7 supplies considerable back tension. Further cleaning of bond-inhibiting films is accomplished by heating in room atmosphere of the strip 1 between brush 13 and roll 9 with a suificient amount of current to drive off bond-inhibiting films. For example, a temperature of 700 F.l,000 F. in a normal room atmosphere is satisfactory. While electrical heating means is shown, other heating means may be employed, such as a protective atmosphere furnace, or other types of cleaning means, e.g., abrading, chemical cleaning, etc. may be employed.

A metallic powder consisting, for example, of a mixture of molybdenum and silver particles, e.g., in the ratio of 60-40 by weight, is fed to the hopper 43. The vibrator 45 causes it to feed down between the strip 1 and the roll 19 at the wrap-around portion of the former. cated at B in FIG. 2, the wrap-around movement involves some bulging effect of the strip as it presses on the powder upon entering the nip space 21. This results in a preliminary compressive action upon the powder by a concave portion of the strip in the groove 27 as the nip space 21 is approached. This offers resistance to loss of powder by back flow. The side walls of the groove 21 at the same time prevent escape by lateral side flow. The powder thus trapped is forced into the rolls along with a base metal. The roll centers are set in relation to each other so that the compression at the nip space 21 is sufiicient to compact the powder into a highly compressed, almost solid mass adhered to the strip 1, resulting in a so-called green bond both between the metallic particles themselves and between them and the strip. The roll pressure for this purpose is ordinarily high enough that some reduction in thickness of the strip l is accomplished at the same time.

The angular relationship D between side walls 31 of the groove 27 facilitates stripping away of the bonded strip from the groove 27, without sticking and hence without damage to the green-bonded material. The finger 49 guides the finished strip from the rolls as it is pulled out, which is preferably at an approximate right angle as shown. An exit speed of 6.5 ft. per min. has been found As indisatisfactory. By a green bond is meant one which is sufficient to facilitate subsequent handling of the strip, as for example, movement of the green-bonded strip around the guide 23 and into the coil 25. In its coil form the strip is heated for a sufficient time at a suitable temperature to sinter it in known manner to convert the green bond into a strong bond. The parameters for compression and sintering are known and require no further comment.

FIG. 4 diagrammatically illustrates a cross section of the green-bonded strip product coming from the rolls l7 and 39. This is composed of the backing strip 1, wherein the nickel component is identified as N and the silver cladding as S. The green-bonded compressed-powder component is identified as P. The places at which these components are located before and after rolling are indicated in FIG. 1 by the letters S, N and P. On the scale of FIG. 1, it is not possible to show layer S, which therefore is not lettered in the green-bonded strip product coming from rolls l7 and 19 in that figure.

In FIG. 5 is illustrated a cross section of a product in which the silver cladding prior to rolling is omitted from strip 1. In this case the compressed powder component P has been located directly upon the nickel base strip. The advantage, however, of the silver cladding S in the case of FIG. 4 is that a green bond between the powder and the backing strip may be obtained with less roll pressure than in the case of FIG. 5.

Examples of compressed powder thicknesses that may be obtained are as follows: .016" thick of powder on a base metal thickness of .067" after bonding. In another case, powder thickness of .023 was obtained upon a base metal .051" after bonding. In another case, at an entry angle of 70 for angle A a powder thickness of .040 was obtained with a base metal thickness of .040".

Other examples of particular materials that may be used are a powder mixture of silver and nickel in the ratio of 60% of silver to of powder by weight, clad on a pure nickel base strip .100" thick and carrying a .002"-.003" cladding of silver. In this example, cleaning was accomplished by heating at 800 F.900 F. The finished product consists of a base material .051" thick carrying a .032" thick layer of the compressed silvernickel powder mixture.

Another example is the use of a powder mixture of 99.5% silver by weight with 050% by weight of graphite bonded to a backing strip composed of by weight of copper to 45% by weight of nickel. In this case, heating was not required for cleaning, simple abrasion by Wire brushing or the like having been sufficient.

As will be seen from the above, an important feature is the wrap-around hugging action of the base metal strip 1 adjacent the tapered bottom of the groove 27 as the nip space 21 between rolls is approached, whereby the rolls are prevented from pushing back and losing powder. It is to be noted in this regard that a considerable part of the desired effect can be obtained by use of the wraparound feature on smooth rolls without the interlocking flange and groove arrangement. However, the grooved and flanged forms of the rolls are desirable for the prevention of edge-cracking. In other words, if some degree of edge-cracking mightbe tolerated, then the rolls may be made straight or flat, i.e., without either flange or groove, while retaining the Wrap-around feature which is responsible for the ability to obtain a larger ratio of powder thickness to thickness of the backing strip.

By means of the invention, powder densities obtained upon green bonding exceed those heretofore obtained by rolling processes; for example, densities of from 98% of the solid forms of the materials being compressed. Such increased densities imply a strip which is much more flexible and with greater green-bonded strength than strips having lower densities in their powder-formed components. Further, by means of the invention substantially uniform powder density transversely as well as longitudinally of the strip is afforded.

In FIGS. 6 and 7 is shown another form of the invention in which the backing strip does not appear in the product. In FIG. 6, like numerals designate like parts. In this case the backing strip which is lettered 2 is endless, being returned from the nip 21 over rollers 55. The strip 2 may, for example, be left uncleaned, and a light surface separating film, e.g., oil, may be provided on the strip so as to discourage the formation of any bond between it and the compressed powder. Thus the only bonding which occurs in the roll nip space 21 is that between the particles of the powder fed in from the hopper 43. The resulting strip that comes from the nip is a strip of green-bonded particles such as illustrated at 4 in FIG. 7. This strip is coiled and subsequently sintered to form the final strip product. In the FIG. 6 arrangement, a brake such as 7 (as shown in FIG. 1) may be used but is not always required because tension may be maintained in the endless strip 2 by properly adjusting the positions of the rolls 55.

In view of the above, it will be seen that, because of the angular entry of the strip 1 to the roll nip 21 in a direction so as partially to wrap around one of the rolls, a higher powder to-backing thickness ratio after bonding can be obtained which may be maintained to close longitudinal tolerances, whether or not the rolls are flanged and grooved. These are important advantages in and of themselves. It will also be seen that tolerances of transverse dimensions are also small and that substantially uniform density is achieved transversely as well as longitudinally of the strip by reason of the confining characteristics of the interlocking roll forms, which contributes to avoiding edge-cracking. In addition, as above made clear, high densities resulting from powder compression are achieved in the bonding pass, with resulting greater flexibility in the finished product, whether in the form shown in FIGS. 4 and 5 or in FIG. 7.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions, products and methods Without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The method of producing from metallic powder a dense metallic strip substantially free of edge cracks; comprising initially advancing a solid metallic backing strip to and through a nip region formed by interdigitating radial flange and groove parts of first and second compression rolls respectively, said advance being directed along a path deviating substantially from a perpendicular to a line between roll centers, said path having a substantial portion thereof in advance of the nip portion extending away from the flange of the second roll and lying in the groove of the first roll, feeding metallic powderinto the groove between the part of the strip lying therein and the bottom and sides of the groove, and substantially squeezing the strip and the powder by the rolls in the nip region to eflect under substantial compression a solid-phase green bond.

2. The method according to claim 1, including the step of subsequently sintering the powder to improve the green bond.

3. The method according to claim 1, including the step of separating the compressed powder as a strip from the backing strip after squeezing and exit from said nip region.

4. The method according to claim 3, including the step of sintering the compressed powder strip after its separation from the backing strip to improve the green bond.

5. Apparatus for producing a compressedmetallicpowder strip; comprising first and second compression rolls, said first roll having a groove, said second roll having a radial flange reaching partially into and transversely interfitting with the groove to form a substantially surrounded nip region on a line joining the roll centers, means for moving a metallic strip toward and through the nip region in a path deviating substantially from a perpendicular to a line between the roll centers, said path having a substantial portion thereof directed away from the flange of the second roll lying in the groove of the first roll, means for feeding a substantial amount of metallic powder between the bottom of the groove, and the portion of said metallic strip lying therein, whereby the compression rolls become operative in the nip region upon said substantial amount of powder to effect high compression and a solid-phase green bond between powder particles.

6. Apparatus according to claim 5, wherein the sides of said groove not reached by said flange flare outwardly from the bottom of the groove, whereby edge cracking of the green-bounded strip is minimized and whereby upon exit from the nip region said green-bonded strip may be more readily removed from the groove.

References Jilted in the file of this patent UNITED STATES PATENTS 2,290,338 Koehring Iuly2l, 1942 2,341,732 Marvin Feb. 15, 1944 2,372,607 Schwarzkopf Mar. 27, 1945 2,582,744 Brennan Jan. 15," 1952 2,746,741 Naeser May 22, 1957 T 2,811,750 Cofek Nov. 5, 1957 2,917,821 .Fritsch Dec. 22, 1959 3,019,487 Naeser Feb. 6, 1962 FOREIGN PATENTS 784,153 Great Britain Oct. 2, 1957 799,946 Great Britain Aug. 13, 1958 

1. THE METHOD OF PRODUCING FROM METALLIC POWDER A DENSE METALLIC STRIP SUBSTANTIALLY FREE OF EDGE CRACKS; COMPRISING INTIALLY ADVANCING A SOLID METALLIC BACKING STRIP TO AND THROUGH A NIP REGION FORMED BY INTERDIGITATING RADIAL FLANGE AND GROOVE PARTS OF FIRST AND SECOND COMPRESSION ROLLS RESPECTIVELY, SAID ADVANCE BEING DIRECTED ALONG A PATH DEVIATING SUBSTANTIALLY FROM A PERPENDICULAR TO A LINE BETWEEN ROLL CENTERS, SAID PATH HAVING A SUBSTANTIAL PORTION THEREOF IN ADVANCE OF THE NIP PORTION EXTENDING AWAY FROM THE FLANGE OF THE SECOND ROLL AND LYING IN THE GROOVE OF THE FIRST ROLL, FEEDING METALLIC POWDER INTO THE GROOVE BETWEEN THE PART OF THE STRIP LYING THEREIN AND THE BOTTOM AND SIDES OF THE GROOVE, AND SUBSTANTIALLY SQUEEZING THE STRIP AND THE POWDER BY THE ROLLS IN THE NIP REGION TO EFFECT UNDER SUBSTANTIAL COMPRESSION A SOLID-PHASE GREEN BOND. 